1. Field of the Invention
The present invention relates to acrylic resin expanded beads, acrylic resin expandable beads, and a method for manufacturing a foamed molded article of acrylic resin expanded beads.
2. Description of the Related Art
A model composed of a foamed molded article obtained by filling a metal mold cavity with polystyrene resin expanded beads and heating and molding the beads has been used in the past in a full-mold casting method in which a model is placed in a casting mold, molten metal is allowed to flow into the mold, and a casting is produced while replacing the model in the casting mold with molten metal. With a model of a very large casting, such as a ship's propeller or a press mold, a plurality of foamed molded articles that have a length of 1 or 2 meters, a width of 1 meter, and a thickness of 50 cm (hereinafter such foamed molded articles will be referred to as block foamed molded articles), for instance, are pieced together with an adhesive agent, machined into a large, cuboid foamed molded article of the desired size, and then precisely cut into the desired shape with a milling machine. However, a problem encountered with a full-mold casting method that makes use of a model composed of a foamed molded article of a polystyrene resin is that the polystyrene resin foamed molded article is pyrolyzed and generates soot upon contact with the molten metal during casting, and this soot tends to become admixed in the casting and produce carbon defects therein. Ways to solve this problem have been discussed in, for example, Japanese Laid-Open Patent Application No. 2001-233986, Japanese Patents No. 2,730,703 and No. 2,632,402, which disclose an acrylic resin foamed molded article in which the base resin is a polymethacrylic ester resin that is favorable for use as lost mold or the like in full-mold casting.